Lecture Notes: Basics of Neurons

Introduction

• The neuron is the basic unit of the nervous system.
• Example: Nematode worm has 302 neurons; humans have 100 billion neurons mainly in the central nervous system (brain and spinal cord).

Neuron Anatomy

• Cell Body: Central part of the neuron, typical cell structure with nucleus, Golgi apparatus, mitochondria.
• Dendrites: Extensions from the cell body, receive information in the form of neurotransmitters.
• Axon: Transmits information, begins at the axon hillock and ends at the terminals.
  • Myelin Sheath: Some axons are wrapped in myelin sheaths (Schwann cells) to insulate and speed up transmission.
  • Nerve Fiber: An axon wrapped in myelin sheath.
• Synapse: Gap between neurons where information is transmitted.

Neuron Classification

Structural Classification

1. Multipolar Neurons:
   • Multiple dendrites, one axon.
   • Most common type in the body.
2. Bipolar Neurons:
   • One dendrite, one axon.
   • Rare, found in sensory organs like eyes and nose.
3. Unipolar Neurons:
   • Fused axon and dendrite.
   • Common in sensory neurons transmitting to the CNS.
4. Axonic Neurons:
   • No axon.
   • Found in the brain, functionality not well understood.

Functional Classification

• Sensory Neurons (Afferent Neurons):
  • Transmit sensory information from receptors (e.g., skin receptors) to the CNS.
• Motor Neurons (Efferent Neurons):
  • Send information from the CNS to effectors (muscles, glands).
• Interneurons:
  • Connect sensory and motor neurons and other neurons in the CNS.

Summary

• Review the structure and types of neurons.
• Understand the pathways and functions of different neuron types in the nervous system.

Note: For detailed explanations, refer to accompanying videos on action potentials and synapse functions. Rewind and review specific sections if needed to reinforce understanding.